Portion of a mask cushion



FIG. 1 is a perspective view of a portion of a mask cushion according to of our design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a left side view thereof; and,

FIG. 5 is a rear view thereof.

Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design. Where included, dotted lines represent the border between claimed and non-claimed subject matter and form no part of the claimed design.

The use of stippling is used to indicate shading. 

The ornamental design for a portion of a mask cushion, as shown and described. 